A valve control system of the stated type is known from DE 10 2008 005 292 A1. The valve control system has an adjustable camshaft, and the adjustable camshaft is composed of an outer shaft and an inner shaft, and cam elements are rotatably accommodated on the outer shaft, which elements are connected with the inner shaft by way of bolts. When the inner shaft is rotated in the outer shaft, the cam elements on the outer shaft rotate together with the inner shaft. Furthermore, firmly disposed cam elements are situated on the outer shaft, and when the inner shaft is rotated in the outer shaft during operation of the valve control system, by a phase shifter, the control times of inlet valves and outlet valves, for example, can be determined separately in this manner.
The phase shifter serves to rotate the inner shaft in the outer shaft. The phase shifter comprises a first control element, formed by a stator, and a second control element, formed by a rotor, which is accommodated in the stator so as to rotate. Multiple vane elements are disposed on the rotor, and the vane elements can be hydraulically impacted in vane cells, so that rotation of the second control element, in other words the rotor, in the first control element, in other words the stator, is made possible.
By means of coupling the first control element, for example with the outer shaft, and the second control element, for example with the inner shaft, the rotation of the second control element in the first control element is transferred to the adjustable camshaft.
During operation of a valve control system having an adjustable camshaft and having a phase shifter, rotation of the inner shaft in the outer shaft frequently occurs during a very short time; this is made possible by a correspondingly strong hydraulic action on the vane elements in the hydraulic vane cells. It is disadvantageous that in this regard, harmful contact of the vane elements with what are called early and late stops can come about, and the stops are formed by the walls of the chambers in the stator. Specifically if large adjustment angles are required, vane elements that have a relatively thin structure must be affixed to the rotor. Vane elements that have a particularly thin structure can experience damage if strong fluid action is required for very short-term adjustment of the rotational position of the inner shaft in the outer shaft.
Furthermore, adjustable camshafts have bolts for connecting the rotatable cam elements with the inner shaft, and the bolts are passed through passages in the outer shaft. These passages have a restricted elongated expanse in the circumference direction of the outer shaft, and the bolts can be rotated in the passages over the desired angle of rotation. In this regard, the bolts can make contact with the end regions of the passages, and this can also cause damage of the adjustable camshaft, so that contact of the bolts with the passages should be avoided.